In mobile communications systems, the Short Message Service (SMS) transfers short messages between an initiating user's communication device (“IUMD” in the figures) and an intended recipient user's communication device (“IRUMD” in the figures) via a service center (“SC” in the figures). The service center serves as an interworking and relaying function for the message transfer between the IUMD and IRUMD. There are two basic services associated with the short message point-to-point services: SM MT (short message mobile terminated) and SM MO (short message mobile originated). In SM MT, the system transfers a short message from the service center to a mobile station. In SM MO, the system transfers a short message from the IUMD to IRUMD via a service center. In either case, the system provides information about the delivery of the short message either by a delivery report or a failure report. The text messages transferred by the short messages contain up to 140 octets (bytes).
One of the primary characteristics of the SMS system is that it is a store and forward communication system. Thus, a SMS communication system does not rely on real-time connectivity between the sender and the receiver. A SMS message can be transmitted to a recipient at any time, even when the recipient's communication device (mobile station or short messaging entity) is turned off or otherwise not logged into the system. An active mobile station can receive a short message (SMS DELIVER) at any time, independently of whether or not there is a speech or data call in progress. If a recipient mobile station was turned off when a message was initially sent, it will receive the message as soon as it is activated and logged onto the communication network. A report is returned to the service center confirming that the mobile station has received the message or not. Similarly, an active mobile station is able to submit a short message (SMS-SUBMIT) at any time, independently of whether or not there is a speech or data call in progress. A report is always returned to the mobile station, confirming that the service center has received the message or not. Similar reporting is provided for other types of messaging systems, such as multimedia message system (MMS) messages.
When the service center sends a pager mode type instant message (IM) the message may not be delivered to the intended recipient user, depending on the intended recipient user's status. For example, if the intended recipient user is offline an IM message will not be delivered because the IM system protocol is not a store-and-forward communication system. On the other hand, if an IM message is forwarded on to a recipient on a SMS communication system, the mechanism for conveying the message across the two communication protocols, referred to generally herein as a protocol-to-protocol interface gateway, can result in a false delivery indication. For example, to convey an IM message through a SMS system, the IM message may be forwarded via an instant messaging protocol (IM) to short message (SM) protocol interface gateway (IP-SM-GW). If the recipient mobile device is offline at the time, the IM message may be forwarded to an IM server/storage by the IP-SM-GW until the user is available. In this case the IM server/storage sends a 2xx status message (Success message), for example, 202 ACCEPTED message, to the IP-SM-GW indicating that the IM message has been received. In response the IP-SM-GW will generate a Delivery Acknowledgement message which is sent to the IM originator. However, this delivery acknowledgement is erroneous because it does not represent the true state of the intended recipient user (i.e., intended recipient user or intended recipient user equipment IRUE) in many cases. This false delivery acknowledgement is a problem that limits the usefulness of communicating non-store-and-forward type messages over store-and-forward communication systems.